My son who was awarded a scholarship at the first board dressed in a suit for his interview (coat and tie is probably fine too). Some of the questions came from his resume (asked to talk more about specific items on his resume). He was also asked why he wanted NROTC and then he was given some ethical dilemma situations and asked how he would handle them. Hope that helps and good luck!

+1 to @USMCGrunt. Read not only the threads about ROTC interviews but also those about nomination interviews and BGO interviews. Same type of questions all around. More information than you can shake a stick at. Best wishes.